An exhaust fluid treatment apparatus may comprise a plurality of modules, wherein each module is intended to treat one or more constituents of an exhaust fluid. The modules may be arranged in series such that exhaust fluid flows through each module in sequence. In order to operate as intended, some modules may require the exhaust fluid to exceed a particular temperature.
An exhaust fluid treatment apparatus may comprise a diesel oxidation catalyst module and a selective catalytic reduction module, downstream of the diesel oxidation catalyst module. The selective catalytic reduction module may not operate as intended when the exhaust fluid is below a certain temperature. In order to increase the temperature of the exhaust fluid in the selective catalytic reduction module, it may be appropriate to use the diesel oxidation catalyst module to increase the temperature of the exhaust fluid passing through it in order to increase the temperature of exhaust fluid arriving at the selective catalytic reduction module. This may be achieved by introducing unburnt fuel upstream of the diesel oxidation catalyst for oxidation in the diesel oxidation catalyst thereby to increase the temperature of the exhaust fluid leaving the diesel oxidation catalyst module. However, it may be necessary to avoid injecting unburnt fuel into the diesel oxidation catalyst module if the temperature of the diesel oxidation catalyst module is too low to result in combustion of the fuel since otherwise the unburnt fuel may simply pass out of the diesel oxidation catalyst module and may thereby cause damage to subsequent features of the exhaust fluid treatment apparatus and/or pass directly to atmosphere.
Against this background there is provided a method of controlling operation of an exhaust fluid treatment apparatus.